In relation to the structure of a conveyor belt, reference is made in particular to the following patent literature:
DE 25 20 943 A1DE 38 01 120 A1DE 25 32 190 A1U.S. Pat. No. 5,460,261DE 44 36 042 A1U.S. Pat. No. 5,609,242EP 0 336 385 A1WO 2008/034483 A1
The carrying-side cover plate and the running-side cover plate normally each comprise a rubber mixture containing a rubber component or a rubber component blend, a wetting agent or a wetting system, comprising a wetting agent and an accelerator, and also normally further mixing ingredients, in particular a filler and/or a processing aid and/or an aging prevention aid and/or a plasticizer and/or other additives (for example, fibers, colored pigments). The relevant rubber basis is in particular:    natural rubber (NR)    butadiene rubber (BR)    chloroprene rubber (CR)    styrene-butadiene rubber (SBR)    nitrile rubber (NBR)    butyl rubber (IIR)    ethylene-propylene rubber (EPM)    ethylene-propylene-diene rubber (EPDM)    SBR/NR blend    SBR/BR blend    NR/BR blend
Of particular importance hitherto has been CR, which is distinguished by high resistance to flames, weathering and aging, in particular for conveyor belts with use in underground mining. Furthermore, NR and the aforementioned blends (DE 10 2009 043 904 A1) have gained greater importance in open-cast mining.
As a result of the vulcanization of a rubber mixture of the aforementioned type, the conveyor belt acquires the required elastic properties.
The embedded tension members used which run in the longitudinal direction of the conveyor belt are cords made of steel or aramid, cords made of steel being of particular importance. In particular, in conjunction with steel cord conveyor belts, for the purpose of slit protection, an embedded transverse reinforcement made of synthetic cords, for example of polyamide, is additionally used (WO 2008/034483 A1). The tension members can also be a two-dimensional textile structure, in particular a single-layer or multilayer fabric, for example, a polyester-polyamide fabric.
Normally, the guidance of a conveyor belt in a conveyor system is carried out in open form, specifically within the context of a hollowed carrier roller frame.
In the last 20 years, however, the closed conveyor system using a tubular conveyor belt has also been developed further. The system components in the closed conveyor system, in addition to the drums (drive drum, reversing drum), carrier rollers and carrying frames, are normally also correction rollers and a hold-down roller when the conveyor belt is closed. In this connection, reference is made in particular to the following patent literature:
DE 36 06 129 A1DE 10 2009 003 552 A1DE 36 12 765 A1EP 0 336 385 A1U.S. Pat. No. 5,460,261
Further components of a conveyor system can be a supply chute, discharge chute, deflection drums and chute seals made of a polymer material.
When they are charged with the conveyed material, for example ores, conveyor belts are highly stressed. As a result, damage to the carrying-side cover plate of the conveyor belt often occurs, specifically in the form of cuts, material break-outs or other damage. These are critical to the service life of the conveyor belt and must therefore be detected as early as possible. Wear phenomena as a result of abrasion can also occur in the running-side cover plate with contact with the drums and carrier rollers and possibly with further roller components which are mentioned above. Furthermore, in the case of a steel cord conveyor belt, the running-side cover plate can be slit by the steel cords under extreme loadings, the synthetic cord transverse reinforcement already mentioned offering adequate slit protection—although not always. Finally, the tension members can also be damaged during continuous operation, which can have a detrimental effect on the pulling power of a conveyor belt.
In addition to regular visual inspection, there are various systems for monitoring the condition of the conveyor belt during the operation of a conveyor system. An outline of the relevant prior art is set forth below:    (a) The documents DE 44 44 264 C1, DE 197 15 703 B1, US 2012/0012444, U.S. Pat. No. 6,781,515, U.S. Pat. No. 7,178,663 and U.S. Pat. No. 4,621,727 describe an approach in which the conveyor belts are provided with conductor loops at regular intervals, the damage to which can be detected by electro-inductive measuring methods. Transponders can also be employed instead of the conductor loops or in combination with the latter. The significant conductor loop technology and the problems associated therewith will be discussed in more detail at another point.    (b) DE 195 39 980 A1 and EP 0 787 669 B1 describe a monitoring device using monitoring elements and identification elements which are incorporated into the conveyor belt transversely with respect to the conveying direction and which, as they are led past stationary reading devices, report both the condition and also the position. However, this monitoring concept is very complicated to implement.    (c) U.S. Pat. No. 6,356,201 presents a system for monitoring a layer subjected to wear. For instance, a ferromagnetic layer is embedded in the carrying-side cover plate and/or running-side cover plate and shields the signal from a transporter located underneath unless this layer has been damaged. This monitoring concept is also very complicated and can be applied only to specifically equipped conveyor belts.    (d) Monitoring the condition of the steel cords in conveyor belts is carried out by means of an inductive field that is led past externally (DE 199 21 224 A1) or by means of a magnetic field (DE 10 2006 036 668 A1). The disadvantage is that only damage to the steel cord structures can be registered hereby.    (e) When monitoring the damage to the carrying-side cover plate and/or running-side cover plate, use is made of opto-electronic systems, in particular in the form of a line or surface camera. In this connection, reference can be made in particular to the following patent publications:
DE 24 13 543 A1DE 101 29 091 A1DE 42 40 094 A1DE 101 40 920 A1U.S. Pat. No. 6,702,103EP 1 187 781 B1U.S. Pat. No. 6,831,566U.S. Pat. No. 7,259,854US 2003/000808WO 2008/031648 A1
The comprehensive development work documented above underlines the increasing importance of this monitoring device. In addition to the great technical effort, however, this monitoring concept depends on a conveyor belt surface without significant contamination. For this reason, the opto-electronic system is additionally provided with an air-purge apparatus, but this indicates the limits of the efficiency.    (f) Also known is an apparatus for the non-destructive inspection of a conveyor belt via high-energy rays, in particular x-rays, reference being made in particular to the following patent publications in this connection:
DE 35 17 314 A1JP 04158208 A (Patent Abstracts of Japan)U.S. Pat. No. 8,149,989JP 2000292371 A (Patent Abstracts of Japan)
The disadvantage is that, in the case of such rays, the monitoring system has to be integrated into a housing on safety grounds, which likewise indicates the limits of the efficiency.
Furthermore, in the case of this monitoring device, it is primarily the interior of a conveyor belt, in particular the embedded steel cords, that is registered.
The monitoring of a conveyor belt by means of a slit protection system using the conductor loops already mentioned has gained particular importance; in the following text, the previous slit protection technology will now be discussed in more detail.
A conductor loop or conductor loop packet is a packet which comprises one or more endlessly connected (short-circuited) loops (contours) of any desired form, for example in the form of a meander, rectilinear, rectangular or in the form of a figure 8. The contours can be produced from various materials and constructional elements, for example from a steel cord, a conductive textile thread or a conductive polymer. They are embedded in the polymer packet of the conveyor belt. The conductor loop or the conductor loop packet can be vulcanized into the cover plate of a conveyor belt on the carrying side and/or running side during the production of a conveyor belt or else subsequently, specifically normally at a distance of 50 to 200 m. A conductor loop functions in accordance with the principle of electromagnetic induction. With regard to conductor loop technology and the conductor loop form, reference is made in particular to the following patent publications:
DE 38 11 533 A1DE 199 02 508 A1DE 39 27 746 A1DE 101 00 249 A1DE 40 12 906 A1U.S. Pat. No. 4,621,727DE 40 13 764 A1U.S. Pat. No. 7,178,663DE 40 14 475 A1US 2012/0012444
In the following two published applications, the conductor loop packet is described in particularly detailed form by using frequently used conductor loop forms:
In U.S. Pat. No. 4,621,727, the conductor loop is formed in the shape of a figure 8, specifically within the context of multiple turns.
In U.S. Pat. No. 7,178,663, a conductor loop packet is presented which comprises a first conductor loop. A second conductor loop is arranged inside this first conductor loop. If appropriate, a third conductor loop can be incorporated inside this second conductor loop.
The slit protection system is an electrical system which comprises at least one interrogation station, in particular in the form of a transmitter/receiver pair, at least one slit monitoring station, for example in the form of a scanner, and normally additionally at least one proximity initiator and/or at least one transponder, and functions in accordance with the principle described below.
During the operation of the conveying system, the conductor loops are interrogated by an interrogation station by means of a combination of a transmitter and a receiver and a slit monitoring station. When a conductor loop passes the interrogation station, an electromagnetic signal is transmitted from the transmitter to the receiver by means of an intact contour or contours. The transmitter generates an alternating magnetic field, which generates a current in the conductive short-circuited contours of a conductor loop. This current in turn generates a magnetic field, which is registered by the receiver, that is to say in accordance with the principle of electromagnetic induction. If the conveyor belt is slit in the conveying direction and thus the contour or contours of the conductor loop has or have been destroyed, no signal is transmitted from the transmitter to the receiver. The slit monitoring system sends a signal to the central controller of the conveyor system, in this case the conveyor belt being stopped. As a result, the extent of the damage also remains limited. The position of conductor loops is determined absolutely, irrespective of the conveyor belt speed and the conveyor belt running direction, and relative to the adjacent conductor loops with the aid of at least one proximity initiator which, for example, is located on a drum. There are also solutions for position determination on the basis of at least one transponder. The slit protection system is connected to the central controller of a conveyor system, which controls the entire conveyor system.
The main task of each conductor loop slit protection system consists primarily in stopping a conveyor system if a longitudinal slit or a great amount of conveyor belt damage in the conveying direction arises. Limited conveyor belt notches or perforations must not be the cause of, as a result, a damaged conductor loop becoming a reason for stopping a conveyor system.
Since the contours in a commercially available conductor loop packet, for example following the teaching according to U.S. Pat. No. 4,621,727 and U.S. Pat. No. 7,178,663, are located very close to one another, there is the danger that all the contours of the entire conductor loop package can fail as a result of a single local damage event. Consequently, in the case of such a packet construction, undesired plant stoppages and time losses are to be feared by the conveyor system operator.